1. Field of the Invention
The present invention relates to an image engraving method whereby an image of a license, a card holder or the like is engraved on synthetic paper or a card surface. More particularly, the present invention relates to an image engraving method for improving the engraving efficiency of an engraving machine when identification cards or the like for use in public organizations, banks or the like are produced by engraving a photograph of the face of a card holder or other information (image) on synthetic paper or a card surface.
2. Description of the Related Art
Engravings made on these kinds of conventional cards are for photographs of the face only. A specific example of the construction of an apparatus used for engraving such cards has already been proposed. An example of such an image engraving method is illustrated as a portion of FIG. 2, which also illustrates the apparatus of the present invention.
In FIG. 2, reference numeral 1 denotes an engraving table which reciprocates a given distance horizontally from side to side by a driving motor (not shown); and reference numeral 2 denotes a card for engraving, e.g., a thin plate of vinyl chloride. Black, blue, or other paint is strongly and fixedly applied beforehand on a surface 11 of card 2 where an engraving of a photograph of a face, characters or the like will be made. Reference numeral 3 denotes an engraving needle (stylus); reference numeral 4 denotes an engraving needle driving device for stylus 3. Components 1,2,3 and 4 are common to known engraving devices. The additional elements of FIG. 2 comprise a portion of the present invention. Reference numeral 5 denotes an engraving method discrimination plate of the present invention which reciprocates from side to side together with the engraving table 1. A photodetector unit consisting of a light source 12 provided on one side of the engraving discrimination plate 5 and a phototransistor 6 or the like located on the opposite side of engraving discrimination plate 5. Reference numeral 7 denotes an electronic changeover switch which performs switching according to the output of the photodetector unit. Reference numeral 8 denotes a video camera which generates its video signal and scans a video image (a face of a person or photograph) in synchronization with the movement of the engraving table 1. Camera 8 can alternatively be replaced with a photoelectric converter consisting of a light source, a lens, slits, photoelectric elements, a card scanning apparatus or the like. Reference numeral 9 denotes a video camera or a photoelectric converter for the nondetailed portion of the engraving (characters, symbols, etc.) which is the remainder of the engraved image with the exception of the part consisting of the video image. Video camera or photoelectric converter 9 also scans in synchronization with the movement of the engraving table 1. The output of the video cameras or photoelectric converters 8 and 9 is switched by a switch 7 and output to driving apparatus 4. Reference numeral 10 denotes a modulating apparatus.
In addition to the side-to-side reciprocative movement, the engraving table 1 must be fed in a back and forth direction at right angles to the reciprocative movement. This may be performed by moving the engraving stylus 3 back and forth. The illustration of those devices is omitted. To make the return of the reciprocative movement of the engraving table fast, time is allocated, for example, in such a manner that 3/4 of one reciprocation is for the forward motion and 1/4 thereof is for the return. The time required for the engraving table 1 to make one reciprocation is about 0.8 seconds.
Forgery and alteration of passports, licenses, and identification certificates have occurred many times in recent years. Thus, engraving characters, symbols, etc. in addition to the photograph of the face has become necessary to prevent problems. A discrimination between suitable engraving methods must be made in each case.
There are two methods for engraving cards: line engraving and dot engraving. The merits and demerits of each are shown below:
______________________________________ Line Dot Engraving Engraving ______________________________________ Strokes of engraving needle Long Short Influence of flatness of card Great Small Visual offensiveness of engraving lines Great Small Power required for engraving Small Large ______________________________________
Generally, line engraving is performed in that part where there are characters, symbols, etc., which can be represented by black and white (two levels), and dot engraving is performed in that part where half tones, such as a photograph of a face or the like, are needed.
One method which has been devised for engraving on a card after a discrimination has been made between these two engraving methods is the conventional engraving sweeping method shown in FIG. 3.
In FIG. 3, the slanted lines 14 and 16 indicates scanning lines of an engraving needle (stylus). Engraving is accomplished when a sweeping operation is performed sequentially from 1 to n, and again from n+1 to m. The solid and broken lines of the scanning lines indicate the difference between the contents to be engraved. The solid lines 14 indicates that portion which can be represented by black and white (two levels), such as characters, symbols, patterns, etc., namely, where line engraving should be performed. The broken line 16 indicates that portion where there are many half tones, such as a photograph of a face or the like, namely, where dot engraving should be performed. As described above, a boundary line 18 for discriminating the engraving contents is generally parallel to the short side of the part requiring engraving in the card. Therefore, as shown in FIG. 3, if an engraving is performed while sweeping in a direction substantially parallel to the short side and the boundary line 18, it is possible to manage with only one time, between n and n+1, to switch the engraving method. The above-described conventional image engraving apparatus can be used without modifying it too much. However, sweeping parallel to the short side direction requires a greater number of shorter sweeps than sweeping parallel to the long side.
However, in the production of various kinds of engraved cards, the need for shortening the time required for engraving has been high for a long time. To meet this demand, a higher-speed horizontal reciprocative movement of the engraving table must be achieved. One effective means for achieving this is to make the engraving table lighter. But, light weight is limited by the necessity to produce a sturdily constructed engraving table.
Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art by shortening the time required for engraving without diminishing the engraving quality.